1. Technical Field
The present invention relates to a thin film piezoelectric device using a thin film piezoelectric material.
2. Background Art
In recent years, thin film piezoelectric devices using thin film piezoelectric materials instead of using bulk piezoelectric materials have been increasingly put into practical use. Examples of the devices include a gyrosensor, a shock sensor, a microphone, etc., which utilize the piezoelectric effect of converting the force applied to a piezoelectric film into voltage, an actuator, an ink jet head, a speaker, a buzzer, a resonator, etc., which utilize the inverse piezoelectric effect of deforming a piezoelectric film by applying a voltage to the piezoelectric film, and the like.
Use of piezoelectric material thin films can reduce the sizes of devices and thus extend the applicable field, and also permits the batch production of many devices on a substrate, thereby increasing mass productivity. In addition, when sensors are manufactured, the sensors have many advantages in performance, such as an improvement in sensitivity. However, in comparison with bulk materials, thin film materials have large influences on piezoelectric characteristics by the coefficients of thermal expansion of the other layers constituting a device, film physical properties such as Young's modulus, external stress introduced from the other layers, and internal stress possessed by a piezoelectric film, and thus a stress control technique different from that for bulk materials is required. Therefore, a method for controlling piezoelectric characteristics by a stress control technique for piezoelectric films becomes an important factor in designing a thin film piezoelectric device.